parseTimeM succeeds on hours/minutes greater than specified in documentation

[epsilonhalbe]

The documentation for the format strings says

%H
hour of day (24-hour), 0-padded to two chars, 00 - 23
...
%M
minute of hour, 0-padded to two chars, 00 - 59

but while

parseTimeM True defaultTimeLocale "%Y-%m-%d %H:%M" "2017-03-31 23:59" :: Either String UTCTime
parseTimeM True defaultTimeLocale "%Y-%m-%d %H:%M" "2017-02-29 23:59" :: Either String UTCTime

Succeeds/Fails correctly, the following

parseTimeM True defaultTimeLocale "%Y-%m-%d %H:%M" "2017-03-31 23:99" :: Either String UTCTime
parseTimeM True defaultTimeLocale "%Y-%m-%d %H:%M" "2017-03-31 99:59" :: Either String UTCTime
parseTimeM True defaultTimeLocale "%Y-%m-%d %H:%M" "2017-03-31 99:99" :: Either String UTCTime

Succeed - with hours/minutes I would not consider correct.

I would expect parseTimeM to have the property "if it is parseable then the formatted string is equal to the initial string".

import Data.Time
import Test.QuickCheck
import Text.Printf

newtype YmdHMString = YmdHM String deriving Eq

instance Show YmdHMString where
  show (YmdHM s) = s

instance Arbitrary YmdHMString where
  arbitrary = do year   <- getPositive <$> (arbitrary :: Gen (Positive Integer))
                 month  <- choose (00,99) :: Gen Int
                 day    <- choose (00,99) :: Gen Int
                 hour   <- choose (00,99) :: Gen Int
                 minute <- choose (00,99) :: Gen Int
                 return $ YmdHM $ printf "%d-%02d-%02d %02d:%02d"
                                         year month day hour minute

prop_YmdHM (YmdHM s) = let fmt = "%Y-%m-%d %H:%M"
                           time = parseTimeM True defaultTimeLocale fmt s :: Maybe UTCTime
                        in maybe True ((s==).formatTime defaultTimeLocale fmt) time

[epsilonhalbe]

@AshleyYakeley do you think this is an issue or are there cases where the time parser should accept "99:99" as input?

[ghost]

Starting to look briefly at this. I will report back any progress I make.

[epsilonhalbe]

I have a fix for it n my forked repo, but I don't know enough about the quirks of time, and by this i don't mean the library, but what time values are reasonable or not, to file a pull request without any feedback. This is one of the most depended on libraries so i don't want to be hasty with a change, as it possibly affects a lot of people

[ghost]

Okay, I will not look further into this. I am happy to comment on any PRs your make (maybe from a branch to master within your fork as a first pass review?).

[AshleyYakeley]

fix merged